AN247 datasheet(7/32 Pages) MICROCHIP

7 / 32 page

 2003 Microchip Technology Inc.

DS00247A-page 7

AN247

Debugging

For most situations, it is not necessary to have the

bootloader firmware in memory to do debugging of an

application with either the MPLAB ICD 2 or ICE

devices. However, branch statements must be inserted

at the hardware vectors to get to the new designated

vectors. It may also be useful to have the start-up tim-

ing match exactly to the bootloader entry. When devel-

opment of the application is finished, either remove the

branches and rebuild the project, or export only the

memory above the boot block. This code can then be

distributed to those who are updating their firmware.

COMPILE TIME OPTIONS

Compile time options are available to provide initial set-

tings as well as features. Some features require more

memory than others. Compiling certain combinations of

options can actually generate code that is larger than

the designated boot block.

Modes of Operation (Compile Time)

The bootloader can be built to support either one of two

mutually exclusive modes of operation:

• P Mode - Only PUT commands are accepted. The

device will never ‘talk back’ to the source.

• PG Mode - Both PUT and GET are allowed. The

source can actually read out of the target’s

memory as well as write to the target’s memory.

The compile time definition, ALLOW_GET_CMD, selects

the mode.

Self-Verification

The definition, MODE_SELF_VERIFY, enables a

self-verification feature. With this feature, the firmware

reads back the data written to any type of memory (not

Control registers), and it compares the read data with

the source (received) data. A flag is set in a register if

verification failed.

Vectors

The RESET and interrupt vectors can be set to any

location using the following definitions:

• RESET_VECT

• HIGH_INT_VECT

• LOW_INT_VECT

The default values reside at addresses 200h, 208h,

and 218h, outside of the boot block; they parallel the

default PIC18F458 interrupt vectors. If compiling some

features causes the bootloader to be larger than the

boot block, then these vectors must be adjusted to

addresses above the used memory area. If the jump is

farther than a relative branch, then the definition,

NEAR_JUMP

, must be removed.

Other Basic Settings

There are several other definitions that set CAN

specific settings. These determine which bits of the

message identifier are used for the PUT/GET and

CONTROL/DATA commands, the CONTROL/DATA bit

used for GET responses, as well as the filters and

masks for the programming node. Refer to Table 3 for

specific details.

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